The present invention relates generally to a compressor capable of adjustment of compression capacity or delivery, wherein discharge valves disposed in one of the front or rear discharge chambers are selectively placed in an operative or an inoperative position at which the appropriate front or rear discharge valves are operative or inoperative to perform their normal valving function of closing and opening the corresponding discharge ports communicating with the appropriate front or rear discharge chamber and compression chambers. More particularly, the invention is concerned with improvements in association with a delivery-adjusting mechanism which is adapted to control the position of the appropriate front or rear discharge valves in response to variation in cooling load applied to the compressor.
In the art of variable-delivery compressors of different types, various delivery adjusting mechanisms or devices are known for changing the delivery or displacement of a fluid without intermittent activation of the compressor by means of a disconnectable coupling such as an electromagnetic clutch disposed between the compressor and its drive source. In a refrigerant compressor of a swashplate type, for example, a mechanism for partially and temporarily disabling the compressor (hereinafter referred to as "disabling mechanism") is known according to Japanese Patent Application filed in the name of the assignee of the present application and laid open in 1982 under Publication No. 57-73877, which is also referred to in U.S. patent applications, Ser. No. 556,163 filed Nov. 29, 1983, and Ser. No. 589,871 filed Mar. 15, 1984, both assigned to the assignee of the present application. In the swashplate type compressor disclosed in the Publication No. 57-73877, a pair of opposed discharge chambers, front and rear, are provided adjacent to the ends of respective front and rear compression chambers which are separated by a central swashplate chamber in which a swashplate is disposed. There is also provided a disabling mechanism in association with one of the front or rear discharge chambers, for example, with the rear discharge chamber.
For example, such a disabling mechanism uses a delivery-adjusting valving member having the rear discharge valves which radially extend from the center of the valving member. This valving member is carried by an actuator which is movable axially of the compressor, between its first position adjacent to a rear valve plate in which discharge ports are formed, and its second position axially spaced from the first position. With the actuator placed in the first position, the rear discharge valves on the valving member are rendered operative to perform their normal valving function, permitting closure and opening of the rear discharge ports. In the second position, the rear discharge valves are rendered inoperative. While the compressor is at rest or operating under a low cooling load, the actuator is located, under action of biasing means, at its second position, with the discharge valves separated from the rear valve plate, thereby disabling the rear side of the compressor (rear compression chambers) from effecting a normal compressing operation, whereby the compressor is operated in the 50%-capacity mode. Upon increase of the cooling load, the actuator carrying the valving member is moved against the biasing force to the first position with a discharge pressure of the compressor applied to a specially provided pressure chamber to which the rear side of the actuator is exposed, whereby the rear discharge valves are rendered operative, and consequently the compressor is operable in its 100%-capacity mode.
Such a disabling or delivery-adjusting mechanism, however, suffers the following inconvenience when the rear discharge valves on the delivery-adjusting valving member are moved from their operative position to their inoperative position, i.e., when the compressor is switched from its 100%-capacity mode to its 50%-capacity mode.
When the actuator is started to move toward its second position to separate the rear discharge valves away from the opposite surface of the rear valve plate in order to keep open the rear discharge ports, the fixed end portions of the rear discharge valves which consist of the central base portion of the valving member are forced to be separated away from the rear valve plate. At this time, however, the pressure in a substantive number of the compression chambers (not all compression chambers) is lower than the pressure in the rear discharge chamber because the double-headed pistons in those compression chambers are more or less in their sucking stroke or in an initial stage of their compression stroke at the moment when the actuator starts to move away from the rear valve plate. Consequently, the free end portions and the adjacent intermediate portions of the rear discharge valves corresponding to those compression chambers tend to remain in contact with the rear valve plate while the fixed end portions of the same are forcibly separated from the rear valve plate. This will result in a local stress being exerted on the rear discharge valves between their fixed and free end portions, thereby causing a bending, flexure or deformation of these valves. As a result, repeated movements of the actuator and consequent bending actions of the rear discharge valves will lead to permanent deformation or even fracture of the rear discharge valves, which prevents normal functioning of the valves.
The above indicated phenomenon of the bending actions of the rear discharge valves is aggravated in the case where a pressure relief opening is provided in an central portion of the rear valve plate. Stated in more detail, the central pressure relief opening is formed opposite to the delivery-adjusting valving member which has the rear discharge valves, so that it communicates at its one end with the rear discharge chamber and at the other end with a suction space in the cylinder block and consequently with a suction inlet of the compressor. When the valving member is placed in the operative position with the actuator held in the first position, the pressure relief opening is closed by the central base portion of the valving member. In this condition, the base portion of the valving member (fixed end portions of the rear discharge valves) is held in pressed contact with the rear valve plate because the pressure in the rear discharge chamber is higher than that in the suction space in the cylinder block. Therefore, the radially inward intermediate portions of the rear discharge valves adjacent to the central base portion of the valving member are held in pressed contact with the rear valve plate. Thus, while the actuator is placed in the first position, the rear discharge valves are pressed, over a substantive area thereof, on the rear valve plate under the pressure in the rear discharge chamber. This will cause an increased tendency of flexure or bending of the rear discharge valves when they are separated from the valve plate by the actuator.
A further cause for bending actions of the rear discharge valves is an instantaneous pressure difference within the rear discharge chamber immediately after the actuator is moved toward its second position. When the central base portion of the valving member (fixed end portions of the rear discharge valves) is forcibly separated from the rear valve plate, the rear discharge chamber is brought into communication with the suction space through the open pressure relief opening. Accordingly, a radially inner portion of the rear discharge chamber adjacent to the central portion of the valving member is immediately subjected to a suction pressure in the suction space. Thus, the pressure in the inner portion of the rear discharge chamber suddenly drops to a considerable extent. On the other hand, the pressure in a radially outer portion of the rear discharge chamber adjacent to the free end portions of the rear discharge valves will tend to remain at the level immediately before the actuator is started to move. Thus, there arises an instantaneous pressure difference, between the radially inner and outer portions of the rear discharge chamber. That is, a higher pressure is applied to the free end portions of the rear discharge valves so as to keep them in contact with the rear valve plate.
As described above, the delivery-adjusting or disabling mechanism used in the known variable-delivery compressor is damaged by the respective separation of the delivery-adjusting discharge valves from the corresponding valve plate. This will result in reduced durability and reliability of the delivery-adjusting mechanism and consequently of the compressor.